This invention relates to a system for integrally controlling an automatic transmission and an engine. More particularly it relates to improvements in a system for controlling an automatic transmission and an engine, wherein gear stages are automatically switched in accordance with a preset shift map, and engine torque is changed by a predetermined value during shifting to maintain satisfactory shift characteristics.
Automatic transmissions are known to include gear transmission mechanisms, a plurality of frictionally engaging devices, and hydraulic pressure control devices operated to selectively switch the engagements of the frictionally engaging devices, so that any one of a plurality of gear stages can be achieved in accordance with a preset shift map.
Furthermore, in an automatic transmission for a vehicle, of the type described, there have been proposed various systems for integrally controlling an automatic transmission and an engine, wherein, engine torque is changed during shifting to obtain satisfactory shift characteristics and durability of the frictionally engaging devices (For example, Japanese Patent Laid-Open No. 69738/1980 corresponding to U.S. Patent 4,266,447). More specifically, the system for integrally controlling the automatic transmission and the engine, of the type described intends that the amount of torque transmitted from the engine is changed during shifting and the amount of absorbed energy in various members in the automatic transmission or in the frictionally engaging devices for controlling these members is controlled so as to complete a shifting within a short period of time under a low shift shock, whereby a satisfactory shift feeling is given to a driver and durability of the frictionally engaging devices is improved. As a method of changing (decreasing) engine torque, there is a method of delaying ignition timing of the engine (a method of lag angle).
However, when the method of delaying ignition timing is adopted as a measure of changing (decreasing) engine torque for example, the occurrence of so-called after-burn is increased, which is caused by opening an exhaust valve before the gaseous mixture completely burns in the engine cylinders due to the delay of ignition timing. As a result, such a problem is presented that high temperature gas is exhausted into an exhaust pipe, whereby temperature of an exhaust system (exhaust gas temperature, catalyst temperature, exhaust pipe temperature and the like) rises. The rise in the temperature of the exhaust system caused by changes in engine torque during shifting as described above presents no problem, as far as shift frequency during normal running.
However, in the case of running in the mountainous district where the shift frequency is high or in the case where a user intentionally performs on-off operations of an accelerator, the temperature of the exhaust system rises to a tolerance value or more, and, in an extreme case, an adverse influence is rendered to the durability of an exhaust manifold, and further, in an engine system having turbo-charger, there is a possibility of giving an adverse influence to turbine blades on the exhaust side.
As a consequence, there has heretofore been a need to pay attention to avoid the above-described disadvantages, even if shifting is made under the highest frequency, in designing routines relating to engine torque control, in setting a map of an engine torque change value and the like. For example, the smaller the lag angle value of ignition timing, the smaller the increase of the temperature.
However, when a lag angle value of ignition timing is set at a value rather low from the above-described viewpoint for example, a lowered value of engine torque should naturally be decreased, thus presenting such a problem that the proper purpose of control for improving the shift characteristics including durability of the frictionally engaging devices cannot be satisfactorily displayed in normal time.
In view of the above-described conventional problem, the applicant previously proposed systems for integrally controlling an automatic transmission and an engine, wherein, in controlling an engine torque during shifting, when there is possibility of an actual occurrence of the problem, i.e. when a frequency of shifts is high, the shifting is regulated, so that the freedom in setting the torque control are improved and the proper function of the engine torque control can be satisfactorily displayed in normal time (For example, Japanese patent application No. 290017/1985, Application Date: Dec. 23, 1985, and patent application No. 295198/1985, Application Date: Dec. 27, 1985; which corresponds to the U.S. application Ser. No. 945,501 filed Dec. 23, 1986.
However, when these systems are used, such a disadvantage may occur anew that, if a predetermined period of time or a predetermined number of times for determining the frequency of shifts is set at a definite value, then, even when a lag angle control can be performed without causing a trouble in such a case that the engine is relatively cold, the lag angle control is still regulated.